This project is devoted to the investigation of the functioning of lysosomes. Through study of the lysosomal, cytosolic, and Golgi alpha-D-mannosidases we hope to uncover interrelationships among enzymes of the three cell compartments as well as unique roles of these enzymes. Extensive substrate specificity studies are planned. Experiments with an Acanthamoeba system which we have found allows phagolysosome fusion to occur in vitro will hopefully permit the identification of membrane and environmental factors which determine the specificity of the fusion among these vacuoles. The information obtained should contribute to our understanding of the intracellular dynamics of the lysosomal system. Recent progress includes the development of a light microscopic assay for fusion, which is much faster than the electron microscopic assay used previously. BIBLIOGRAPHIC REFERENCES: Oates, P. J. and Touster, O. "In Vitro Fusion of Acanthamoeba Phagolysosomes" J. Cell Biol. 68: 319-338 (1976). Shoup, V. A. and Touster, O. "The Purification and Characterization of the alpha-D-Mannosidase of Rat Liver Cytosol" J. Biol. Chem. 251: 3845-3852 (1976). Oates, P. J. and Touster, O. "A New Method for Preparing Subcellular Materials for Quantitative Measurements by Electron Microscopy" J. Cell Biol. 70, 206a (1976) Abstract).